From Halopedia, the Halo wiki
UNSC Marine Corps
L. P. B. was a UNSC Marine infantryman who participated in an engagement against the Covenant during the Human-Covenant War. He, L. Jenkins, and one other Marine apparently dodged a thrown Type-1 Antipersonnel Grenade during that engagement.
His name is a reference to the term "low ping bastard", a nickname for users who produce lag during multiplayer games.